A conventional door-opening device, which includes a retractable pin disposed to a door and a turnable plate disposed on a housing, has been disclosed in Patent Document 1. The turnable plate has a spiral slot formed therein and is configured to be stably set in both of a position with the opening of the spiral slot directed to a front direction (standby position) and a position with the opening of the spiral slot directed to a depth direction (turned position) by a spring, which has one end fixed at a position away from the pivot thereof and the other end fixed to the housing. When the door is swung toward to a closed position, the retractable pin enters the spiral slot of the turnable plate set in the standby position, and the turnable plate is turned toward the turned position. When the turnable plate is turned beyond the maximum extension of the spring, the turnable plate is forcibly turned toward the rotated position under the action of the spring. Thus, the door is swung toward the closed position, i.e. a position to close the opening of the housing and is set in the closed position.
However, the device disclosed in Patent Document 1 has a first problem in that it is in such a dilemma that if an attempt is made to increase the damping force of a damper for damping a swinging operation in order to absorb impact caused during swinging the door toward the closed position, the resistance to the swinging operation of the door toward the closed position increases while if an attempt is made to decrease the resistance, it is difficult to properly absorb the impact caused when the door is swung hard. The device has a second problem in that in a case where the turnable plate has been turned into the turned position for some reason with the door opened; even if the door is closed, the retractable pin is prevented from entering the spiral slot of the turnable plate set in the turned position, which leads to operation wherein the turnable plate is required to be returned to the standby position. The device has a third problem in that since the retractable pin is disposed on a free end of the door, the device cannot withdraw the door until just before the door is about to be closed. The device has a fourth problem in that the turnable plate and the damper for damping a swinging operation need to have a certain depth for installation since the damping force is generated by bringing a gear disposed in the damper into direct engagement with a sector gear formed on the turnable plate.
Patent Document 1: JP-A-2005-127527 (See Paragraphs 0080 and 0081, and FIG. 30 to FIG. 32)